System and method for keeping a vehicle in a lane

ABSTRACT

The present invention relates, in general, to a system and method for keeping a vehicle in a lane in consideration of a steering wheel contortion angle, and more particularly, to a system for keeping a vehicle in a lane in consideration of a steering wheel contortion angle, which estimates the path of a vehicle in consideration of a steering wheel contortion angle attributable to the distortion of a steering shaft, thus improving the safety and riding comfort of occupants.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims under 35 U.S.C. §119(a) priority to KoreanApplication No. 10-2007-0129793, filed on Dec. 13, 2007, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a system designed to keepa vehicle within its lane. More particularly, the present inventionrelates to a system and method for keeping a vehicle in a lane inconsideration the contortion angle of a steering wheel, where the angleof the steering wheel occurs due to the distortion of a steering shaftattributable to the vehicle aging or deteriorating durability.

2. Background Art

It can be the case that when a vehicle is used for a long period oftime, the durability of certain components of the vehicle are weakened,and gradual deformation may occur in mechanical assembly of thecomponents that were implemented in an initial production stage. Inparticular, for vehicle safety, steering wheel function may beimportant. It can be the case with a steering wheel that the steeringwheel becomes distorted due to the aging of a vehicle. Consequently, asteering wheel contortion angle occurs due to such distortion of thesteering wheel, and this distortion may also influence the steeringcontrol system, and thus result in errors in keeping the vehicle insideits lane.

The above information disclosed in this the Background section is onlyfor enhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a system and method forkeeping a vehicle in a lane in consideration of a steering wheelcontortion angle attributable to the distortion of a steering shaft.

In particular embodiments, the present invention preferably provides asystem for keeping a vehicle within a lane in consideration of asteering wheel contortion angle, comprising an input informationgeneration unit for measuring variables for dynamic characteristics of avehicle, and suitably estimating information about lateral motion of thevehicle using the variables for dynamic characteristics of the vehicle;a steering wheel contortion angle calculation unit for calculating asteering wheel contortion angle δ_(o) using variables for dynamiccharacteristics of the vehicle and information about lateral motion ofthe vehicle, which are provided by the input information generationunit; and a control unit for suitably calculating a desired yaw rateγ_(d) using variables for dynamic characteristics of the vehicle andinformation about lateral motion of the vehicle which are provided bythe input information generation unit, and calculating a commandsteering wheel angle δ_(fo) using the desired yaw rate and theinformation about lateral motion of the vehicle, and generating acompensated command steering wheel angle, which is a sum of the commandsteering wheel angle and the steering wheel contortion angle which isprovided by the steering wheel contortion angle calculation unit.

Preferably, in certain embodiments, the input information generationunit comprises a sensor unit for suitably measuring variables fordynamic characteristics of the vehicle; a vehicle location and roadcurvature calculation unit for calculating a location of the vehicle, aroad curvature ρ_(ref) and a path error d_(s) using the variables fordynamic characteristics of the vehicle which are provided by the sensorunit; and a Kalman estimator for estimating information about lateralmotion of the vehicle using the variables for dynamic characteristics ofthe vehicle which are provided by the sensor unit and the road curvatureand the path error which are provided the vehicle location and roadcurvature calculation unit.

Preferably, in other certain embodiments, the variables for dynamiccharacteristics measured by the sensor unit include information about aroad along which the vehicle is traveling, Global Positioning System(GPS) information of the vehicle, a speed of the vehicle V, a measuredyaw rate of the vehicle γ, a steering wheel angle δ_(f), and a side slipangle β.

Preferably, in still other embodiments, information about lateral motionof the vehicle estimated by the Kalman estimator include the side slipangle β, the measured yaw rate of the vehicle γ, the path error d_(s)and a relative path angle Δψ.

Preferably, the Kalman estimator realizes an observer equation

$\left( {\overset{.}{\hat{x}} = {{\left( {A - {LC}} \right)\hat{x}} + {Bu} + {Ly}}} \right)$

that is suitably configured using a state equation ({dot over(x)}=Ax+Bu) represented by the following equation:

$\begin{bmatrix}\overset{.}{\beta} \\\overset{.}{\gamma} \\{\Delta \; \overset{.}{\psi}} \\\overset{.}{ds}\end{bmatrix} = {{\begin{bmatrix}a_{11} & a_{11} & 0 & 0 \\a_{11} & a_{11} & 0 & 0 \\0 & 1 & 0 & 0 \\V & L_{s} & V & 0\end{bmatrix}\begin{bmatrix}\beta \\\gamma \\{\Delta \; \psi} \\{ds}\end{bmatrix}} + {\left\lbrack \begin{matrix}b_{11} & 0 \\b_{21} & 0 \\0 & {- V} \\0 & 0\end{matrix} \right\rbrack \begin{bmatrix}\delta_{f} \\\rho_{ref}\end{bmatrix}}}$

the Kalman estimator receives the steering wheel angle δ_(f), themeasured yaw rate of the vehicle γ from the sensor unit and the roadcurvature ρ_(ref), the path error d_(s) from the vehicle location androad curvature calculation unit, and calculates estimated statevariables by which values of a matrix (A−LC) are negative values, thusestimating the side slip angle β, the measured yaw rate of the vehicleδ, the path error d_(s) and the relative path angle Δψ, where

${a_{11} = {- \frac{C_{f} + C_{r}}{\overset{\sim}{m}V}}},{a_{12} = {{- 1} + \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{\overset{\sim}{m}V^{2}}}},{a_{21} = \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{I_{zz}}},{a_{22} = {- \frac{{C_{r}L_{r}^{2}} + {C_{f}L_{f}^{2}}}{I_{zz}V}}},{b_{11} = \frac{C_{f}}{\overset{\sim}{m}V}},{{{and}\mspace{14mu} b_{21}} = \frac{C_{f}L_{f}}{I_{zz}}},{and}$

where constants of respective elements are defined as follows:

C_(f): cornering stiffness of a front wheel shaft of the vehicle,

L_(f): distance from a center of gravity of the vehicle to the frontwheel shaft,

C_(r): cornering stiffness of a rear wheel shaft of the vehicle,

L_(r): distance from a center of gravity of the vehicle to the rearwheel shaft,

V: vehicle speed,

{tilde over (m)}: virtual vehicle weight (weight of vehicle (m)/roadfriction coefficient (μ)),

L_(s): distance between the center of gravity of the vehicle and a GPSinstalled in the vehicle,

I_(zz): moment of inertia of the vehicle,

δ_(f): steering wheel angle, and

ρ_(ref): lane curvature.

Preferably, in other further embodiments, the steering wheel contortionangle calculation unit calculates the steering wheel contortion angleusing steering wheel angle δ_(f) which is provided by the sensor unitand the side slip angle β, the measured yaw rate of the vehicle γ whichare provided by the Kalman estimator.

Preferably, in still other further embodiments, the steering wheelcontortion angle calculation unit calculates the steering wheelcontortion angle using an observer equation

$\left( {{\overset{\overset{\cdot}{\hat{}}}{x}}_{o} = {{\left( {A_{o} - {L_{o}C_{o}}} \right){\hat{x}}_{o}} + {B_{o}u_{o}} + {L_{o}y_{o}}}} \right)$

of a state equation ({dot over (x)}_(o)=A_(o)x_(o)+B_(o)u_(o), wherey_(o)=C_(o)x_(o)=[0 1 0]x_(o)) represented by the following equation:

$\begin{bmatrix}\overset{\cdot}{\beta} \\\overset{\cdot}{\gamma} \\{\overset{\cdot}{\delta}}_{o}\end{bmatrix} = {{\begin{bmatrix}a_{11} & a_{12} & {- b_{11}} \\a_{21} & a_{22} & {- b_{21}} \\0 & 0 & 0\end{bmatrix}\begin{bmatrix}\beta \\\gamma \\\delta_{0}\end{bmatrix}} + {{\begin{bmatrix}b_{11} \\b_{21} \\0\end{bmatrix}\left\lbrack \delta_{f} \right\rbrack}.}}$

Preferably, in other further embodiments, the control unit includes adesired yaw rate calculation unit for calculating a desired yaw rateγ_(d) on a basis of the speed of the vehicle V which is provided by thesensor unit, information about lateral motion of the vehicle which areprovided by the Kalman estimator, and a predetermined distance L_(s)between a center of gravity of the vehicle and a Global PositioningSystem (GPS) installed in the vehicle;

Preferably, in still other further embodiments, the desired yaw ratecalculation unit includes a first adjustment unit for calculating alateral error value, indicating a lateral deviation from a center lineof the lane, by subtracting the path error d_(s), which is provided bythe Kalman estimator, from a reference path error, and a low pass filterunit for controlling a sudden motion of the vehicle on a basis of thelateral error value which is provided by the first adjustment unit.

Preferably, in other further embodiments, the control unit includes asecond adjustment unit for generating a yaw rate error e_(y)=γ−γ_(d),which is a difference between the desired yaw rate γ_(d), provided bythe desired yaw rate calculation unit, and a measured yaw rate γ,provided by the Kalman estimator; a command steering wheel anglecalculation unit for calculating the command steering wheel angle usingthe yaw rate error e_(γ), provided by the second adjustment unit, andinformation about lateral motion of the vehicle, provided by the Kalmanestimator; and a third adjustment unit for generating the compensatedcommand steering wheel angle, which is the sum of the command steeringwheel angle δ_(fo), provided by the command steering wheel anglecalculation unit, and the steering wheel contortion angle δ_(o),provided by the steering wheel contortion angle calculation unit.

Preferably, in other further embodiments, the system further comprises asteering contortion warning unit for providing a warning for distortionof a steering wheel using any one of a visual manner, an aural manner,and a tactual manner, or a combination thereof if a number of times thatthe steering wheel contortion angle δ_(o) exceeds a predeterminedreference angle is equal to or greater than a predetermined number.

The present invention provides a method for a vehicle to remain in alane in consideration of a steering wheel contortion angle, the methodpreferably comprising the steps of measuring variables for dynamiccharacteristics of a vehicle, and suitably estimating information aboutlateral motion of the vehicle using the variables for dynamiccharacteristics of the vehicle; calculating a steering wheel contortionangle δ_(o) using variables for dynamic characteristics of the vehicleand information about lateral motion of the vehicle; and calculating adesired yaw rate γ_(d) using variables for dynamic characteristics ofthe vehicle and information about lateral motion of the vehicle, andcalculating a command steering wheel angle δ_(fo) using the desired yawrate and the information about lateral motion of the vehicle, andgenerating a compensated command steering wheel angle, which is a sum ofthe command steering wheel angle and the steering wheel contortionangle.

In preferred embodiments, the variables for dynamic characteristicsinclude, but are not only limited to, information about a road alongwhich the vehicle is traveling, Global Positioning System (GPS)information of the vehicle, a speed of the vehicle V, a measured yawrate of the vehicle γ, a steering wheel angle δ_(f), and a side slipangle β, and information about lateral motion of the vehicle, which areestimated by a Kalman estimator, include the side slip angle β, themeasured yaw rate of the vehicle γ, a path error d_(s) and a relativepath angle Δψ.

In further preferred embodiments, the step of calculating the desiredyaw rate γ_(d) further includes a step of calculating a lateral errorvalue, indicating a lateral deviation from a center line of the lane, bysubtracting the path error d_(s), which is provided by the Kalmanestimator, from a reference path error, and a low pass filtering step ofcontrolling a sudden motion of the vehicle on a basis of the lateralerror value.

In still further embodiments, the step of calculating the commandsteering wheel angle δ_(fo) is generating a yaw rate errore_(γ)=γ−γ_(d), which is a difference between the desired yaw rate γ_(d),and the measured yaw rate γ, provided by the Kalman estimator, andcalculating the command steering wheel angle using the yaw rate errore_(γ), and information about lateral motion of the vehicle, provided bythe Kalman estimator.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum).

As referred to herein, a hybrid vehicle is a vehicle that has two ormore sources of power, for example both gasoline-powered andelectric-powered.

The above features and advantages of the present invention will beapparent from or are set forth in more detail in the accompanyingdrawings, which are incorporated in and form a part of thisspecification, and the following Detailed Description, which togetherserve to explain by way of example the principles of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram showing the relationship between a traveling vehicleand a lane;

FIG. 2 is a conceptual diagram showing a system for keeping a laneaccording to the present invention;

FIG. 3 is a diagram showing variation in the path of a vehicle relativeto variation in the constants of a low pass filter unit according to thepresent invention; and

FIG. 4 is a diagram showing the comparison of the path error of aconventional lane-keeping system with the path error of the lane-keepingsystem according to the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described herein, the present invention includes a system for keepinga vehicle in a lane in consideration of a steering wheel contortionangle, comprising an input information generation unit, a steering wheelcontortion angle calculation unit, a control unit for calculating adesired yaw rate γ_(d) using variables for dynamic characteristics ofthe vehicle and information about lateral motion of the vehicle whichare provided by the input information generation unit.

In one embodiment, the input information generation unit is used formeasuring variables for dynamic characteristics of a vehicle using thevariables for dynamic characteristics of the vehicle.

In another embodiment, the input information generation unit is used forestimating information about lateral motion of the vehicle using thevariables for dynamic characteristics of the vehicle.

In another embodiment, the steering wheel contortion angle calculationunit is used for calculating a steering wheel contortion angle δ_(o)using variables for dynamic characteristics of the vehicle andinformation about lateral motion of the vehicle.

In still another embodiment, the variables for dynamic characteristicsof the vehicle and information about lateral motion of the vehicle areprovided by the input information generation unit.

In another further embodiment, the system further comprises calculatinga command steering wheel angle δ_(fo) using the desired yaw rate and theinformation about lateral motion of the vehicle, and generating acompensated command steering wheel angle.

In another embodiment of the invention the compensated command steeringwheel angle is a sum of the command steering wheel angle and thesteering wheel contortion angle, which is provided by the steering wheelcontortion angle calculation unit.

The invention features in other aspects a method for keeping a lane inconsideration of a steering wheel contortion angle, the methodcomprising the steps of measuring variables for dynamic characteristicsof a vehicle, and estimating information about lateral motion of thevehicle using the variables for dynamic characteristics of the vehicle,calculating a steering wheel contortion angle δ_(o) using variables fordynamic characteristics of the vehicle and information about lateralmotion of the vehicle, and calculating a desired yaw rate γ_(d) usingvariables for dynamic characteristics of the vehicle and informationabout lateral motion of the vehicle, and calculating a command steeringwheel angle δ_(fo) using the desired yaw rate and the information aboutlateral motion of the vehicle, and generating a compensated commandsteering wheel angle, which is a sum of the command steering wheel angleand the steering wheel contortion angle.

The present invention also includes a motor vehicle comprising thesystem for keeping a vehicle in a lane in consideration of a steeringwheel contortion angle as described in the aspects herein.

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached exemplary drawings. However, it isapparent that the technical spirit of the present invention is notlimited to the exemplary embodiments of the present invention, and mayextend to the range of equivalents thereof.

FIG. 1 is an exemplary diagram showing the relationship between atraveling vehicle and a lane. Referring to FIG. 1, a sensor unitaccording to the present invention suitably measures a location placedahead of a vehicle by a predetermined distance, which is preferablycalled a measurement location. Suitably, various variables indicatingthe relationship between various lanes and a vehicle can be calculatedon the basis of the measurement location.

In one embodiment, the variables include a path error d_(s) indicating adifference in distance between the measurement location and a relevantlane, a relative path angle Δψ indicating an angle which the vehicleforms with the lane on the basis of the measurement location, a sideslip angle β indicating degrees in which the vehicle travels in atraveling direction and in a lateral direction, and the curvature of thelane ρ_(ref).

FIG. 2 is an exemplary conceptual diagram of a system designed for avehicle to stay in, or keep, a lane according to the present invention.Referring to FIG. 2, the lane-keeping system according to exemplaryembodiments of the present invention may preferably include an inputinformation generation unit for suitably generating input informationsuch as variables for dynamic characteristics of a vehicle andinformation about lateral motion of the vehicle, a steering wheelcontortion angle calculation unit for suitably calculating a steeringwheel contortion angle δ_(o) using input information which are providedby the input information generating unit, and a control unit forsuitably calculating a command steering wheel angle δ_(fo) using inputinformation which are provided by the input information generating unit,and generating a compensated command steering wheel angle, which is asum of the command steering wheel angle and the steering wheelcontortion angle which is suitably provided by the steering wheelcontortion angle calculation unit.

Preferably, the input information generation unit comprises a sensorunit for measuring variables for dynamic characteristics of the vehicle,a vehicle location and road curvature calculation unit for calculating alocation of the vehicle, a road curvature ρ_(ref) and a path error d_(s)using the variables for dynamic characteristics of the vehicle which areprovided by the sensor unit, and a Kalman estimator for suitablyestimating information about lateral motion of the vehicle using thevariables for dynamic characteristics of the vehicle which are providedby the sensor unit and the road curvature and the path error which areprovided the vehicle location and road curvature calculation unit.

According to preferred embodiments of the invention, the sensor unit 11measures variables for dynamic characteristics of the vehicle, requiredin order to control the lane keeping of the vehicle. In furtherparticular embodiments, the variables for dynamic characteristicsmeasured by the sensor unit 11 include, but are not limited to,information about a road along which the vehicle is traveling, GlobalPositioning System (GPS) information of the vehicle (for example, thecurrent location of the vehicle), the speed of the vehicle V, estimatedyaw rate of the vehicle γ, a side slip angle β, a steering wheel angleδ_(f), etc.

The vehicle location and road curvature calculation unit 12 calculatesboth the location of the vehicle and the curvature ρ_(ref) of thecurrent travel lane of the vehicle on the basis of the measuredvariables provided by the sensor unit 11.

In other particular embodiments, the Kalman estimator 13 realizes anobserver equation for estimating information about the lateral motion ofthe vehicle, including, but not limited to, the side slip angle β, themeasured yaw rate of the vehicle γ, the path error d_(s) and a relativepath angle Δψ, using the variables for dynamic characteristics of thevehicle, the location of the vehicle, and the curvature of the travellane, which are provided by the sensor unit 11 and the vehicle locationand road curvature calculation unit 12. In particular embodiments, theKalman estimator can be represented by an observer equation that isconfigured using a state equation given by the following Equation [1],

$\begin{matrix}{{{{\begin{bmatrix}\overset{\cdot}{\beta} \\\overset{\cdot}{\gamma} \\{\Delta \; \overset{\cdot}{\psi}} \\{\overset{\cdot}{d}s}\end{bmatrix}\begin{bmatrix}a_{11} & a_{11} & 0 & 0 \\a_{11} & a_{11} & 0 & 0 \\0 & 1 & 0 & 0 \\V & L_{s} & V & 0\end{bmatrix}}\begin{bmatrix}\beta \\\gamma \\{\Delta \; \psi} \\{ds}\end{bmatrix}} + {\left\lbrack \begin{matrix}b_{11} \\b_{21} \\0 \\0\end{matrix} \middle| \begin{matrix}0 \\0 \\{- V} \\0\end{matrix} \right\rbrack \begin{bmatrix}\delta_{f} \\\rho_{ref}\end{bmatrix}}}{{{{where}\mspace{14mu} a_{11}} = {- \frac{C_{f} + C_{r}}{\overset{\sim}{m}\; V}}},{a_{12} = {{- 1} + \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{\overset{\sim}{m}V^{2}}}},{a_{21} = \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{I_{zz}}},{a_{22} = {- \frac{{C_{r}L_{r}^{2}} + {C_{f}L_{f}^{2}}}{I_{zz}V}}},{b_{11} = \frac{C_{f}}{\overset{\sim}{m}V}},{{{and}{\mspace{14mu} \;}b_{21}} = {\frac{C_{f}L_{f}}{I_{zz}}.}}}} & \lbrack 1\rbrack\end{matrix}$

Further, constants of respective elements can be defined as follows:

C_(f): Cornering stiffness of the front wheel shaft of the vehicle

L_(f): Distance from the center of gravity of the vehicle to the frontwheel shaft

C_(r): Cornering stiffness of the rear wheel shaft of the vehicle

L_(r): Distance from the center of gravity of the vehicle to the rearwheel shaft

V: Speed of the vehicle

{tilde over (m)}: Virtual vehicle weight (weight of vehicle m/roadfriction coefficient μ)

L_(s): Distance between the center of gravity of the vehicle and GPSinstalled in the vehicle

I_(zz): Moment of inertia of the vehicle

δ_(f): Steering wheel angle

ρ_(ref): Curvature of the lane

Equation [1] can be represented by a typical state equation {dot over(x)}=Ax+Bu , which can be represented by an observer equation, that is,

$\overset{\overset{\cdot}{\hat{}}}{x} = {{\left( {A - {LC}} \right)\hat{x}} + {Bu} + {{Ly}.}}$

The Kalman estimator 13 of the present system may preferably receive thesteering wheel angle δ_(f), the measured yaw rate of the vehicle γ fromthe sensor unit 11 and the road curvature ρ_(ref), the path error d_(s)from the vehicle location and road curvature calculation unit 12, andmay calculate estimated state variables by which the eigenvalues of thematrix (A−LC) of the Kalman estimator 13 are negative values. In thisway, the Kalman estimator 13 estimates a side slip angle β, a measuredyaw rate γ, a path error d_(s) and a relative path angle Δψ at eachtime, and then updates them. In particular embodiments, the measured yawrate γ and the path error d_(s), among the state variables estimated bythe Kalman estimator 13, may be identical to the measured valuesprovided by the sensor unit 11.

According to further preferred embodiments of the invention as describedherein, the steering wheel contortion angle calculation unit 30calculates the steering wheel contortion angle δ_(o) using variables fordynamic characteristics of the vehicle and information about lateralmotion of the vehicle, which are suitably provided by the inputinformation generation unit 10.

In particular embodiments, the steering wheel contortion anglecalculation unit 30 calculates a steering wheel contortion angle δ_(o),which appears when wheel alignment is suitably contorted, using the sideslip angle β and the yaw rate γ, which are estimated by the Kalmanestimator 13, and a steering wheel angle δ_(s) measured by the sensorunit. In further preferred embodiments, a steering wheel contortionangle is represented by the following Equation [2].

$\begin{matrix}{\begin{bmatrix}\overset{\cdot}{\beta} \\\overset{\cdot}{\gamma} \\{\overset{\cdot}{\delta}}_{o}\end{bmatrix} = {{\begin{bmatrix}a_{11} & a_{12} & {- b_{11}} \\a_{21} & a_{22} & {- b_{21}} \\0 & 0 & 0\end{bmatrix}\begin{bmatrix}\beta \\\gamma \\\delta_{0}\end{bmatrix}} + {\begin{bmatrix}b_{11} \\b_{21} \\0\end{bmatrix}\left\lbrack \delta_{f} \right\rbrack}}} & \lbrack 2\rbrack\end{matrix}$

In certain embodiments, when a state equation in Equation [2] is {dotover (x)}_(o)=A_(o)x_(o)+B_(o)u_(o), the observer equation correspondingthereto is

${\overset{\overset{\cdot}{\hat{}}}{x}}_{o} = {{\left( {A_{o} - {L_{o}C_{o}}} \right){\hat{x}}_{o}} + {B_{o}u_{o}} + {L_{o}{y_{o}\left( {{{where}\mspace{14mu} y_{o}} = {{C_{o}x_{o}} = \left\lbrack \begin{matrix}0 & 1 & {\left. {\left. 0 \right\rbrack x_{o}} \right).}\end{matrix} \right.}} \right.}}}$

Preferably, the control unit 20 calculates a desired yaw rate γ_(d)using variables for dynamic characteristics of the vehicle andinformation about lateral motion of the vehicle which are preferablyprovided by the input information generation unit 10, and suitablycalculating the command steering wheel angle δ_(fo) using the desiredyaw rate and the information about lateral motion of the vehicle, andgenerating the compensated command steering wheel angle, which is a sumof the command steering wheel angle and the steering wheel contortionangle which is suitably provided by the steering wheel contortion anglecalculation unit 30.

In preferred embodiments of the invention, the control unit 20 includesa desired yaw rate calculation unit 23 for calculating the desired yawrate γ_(d) on a basis of the speed of the vehicle V which is suitablyprovided by the sensor unit 11, information about lateral motion of thevehicle which are suitably provided by the Kalman estimator 13, and apredetermined distance L_(s) between a center of gravity of the vehicleand a Global Positioning System (GPS) suitably installed in the vehicle;

In particular embodiments, the desired yaw rate calculation unit 23 cancalculate the desired yaw rate γ_(d) preferably on the basis of thevehicle speed V, which is suitably provided by the sensor unit 11, theside slip angle β, the relative path angle Δψ, and the path error d_(s),which are estimated by the Kalman estimator 13, and the predetermineddistance L_(s) between the center of gravity of the vehicle and a GPSinstalled in the vehicle. In further preferred embodiments, thecalculated desired yaw rate is given by the following Equation [3],

$\begin{matrix}{\gamma_{d} = {- \frac{{V\left( {\beta + {\Delta \; \psi}} \right)} + {K_{d}d_{s}}}{L_{s}}}} & \lbrack 3\rbrack\end{matrix}$

where K_(d) is a constant.

Preferably, the desired yaw rate calculation unit 23 suitably includes afirst adjustment unit 21 for calculating a lateral error value,indicating a lateral deviation from a center line of the lane, bysubtracting the path error d_(s), which is provided by the Kalmanestimator, from a reference path error, and a low pass filter unit 22for controlling a sudden motion of the vehicle on a basis of the lateralerror value which is suitably provided by the first adjustment unit.

According to further preferred embodiments of the invention, the firstadjustment unit 21 subtracts the path error d_(s), provided by theKalman estimator 13, from a reference path error. Accordingly, infurther embodiments, the first adjustment unit 21 suitably generates anerror value indicating a degree in which a traveling vehicle deviatesfrom the center line of the lane. The reference path error is apredetermined value, which is 0 in general, but it may be another value.

Preferably, the Low Pass Filter (LPF) unit 22 can suitably control thesudden motion of the vehicle on the basis of the lateral error value,which suitably indicates lateral deviation from the center line and isprovided by the first adjustment unit 21. A detailed operation of thisaccording to certain preferred embodiments is described below withreference to exemplary FIG. 3.

FIG. 3 is a diagram showing variation in the path of the vehiclerelative to variation in the constants of the LPF according to preferredembodiments of the present invention. Referring to FIG. 3, when thelateral error value of the vehicle is excessively large at theinitiation of control (when the vehicle excessively deviates from thecenter line), the steering actuator of the vehicle does not rapidlyreact to such an excessively large error value, and causes a largeovershoot, thus decreasing the riding comfort of the vehicle.

Therefore, the LPF unit 22 capable of attenuating such sudden variationis preferably added to the lane-keeping system. Accordingly, acharacteristic equation in an s-plane, indicating the LPF unit 50, ispreferably given by the following Equation [4].

$\begin{matrix}{{M(s)} = \frac{K_{h}}{s + K_{h}}} & \lbrack 4\rbrack\end{matrix}$

Referring to Equation [4], the LPF unit 22 can adjust a degree, in whichthe vehicle returns to the center line of the lane using the constantK_(h). Preferably, according to further embodiments, when the constantK_(h) increases, the vehicle can rapidly return to the center line,whereas, when the constant K_(h) decreases, the vehicle can slowlyreturn to the center line.

According to further embodiments, the control unit 20 preferablyincludes a second adjustment unit 24 for generating a yaw rate errore_(γ)=γ−γ_(d), which is a difference between the desired yaw rate γ_(d),provided by the desired yaw rate calculation unit 23, and the measuredyaw rate γ, provided by the Kalman estimator 13, a command steeringwheel angle calculation unit 25 for calculating the command steeringwheel angle using the yaw rate error e_(γ), provided by the secondadjustment unit, and information about lateral motion of the vehicle,provided by the Kalman estimator 13, and a third adjustment unit 26 forgenerating the compensated command steering wheel angle, which is thesum of the command steering wheel angle δ_(fo), provided by the commandsteering wheel angle calculation unit 25, and the steering wheelcontortion angle δ_(o), provided by the steering wheel contortion anglecalculation unit 30.

Preferably, the second adjustment unit 24 generates the yaw rate errore_(γ)=γ−γ_(d), which is the difference between the desired yaw rateγ_(d) provided by the desired yaw rate calculation unit 23 and themeasured yaw rate γ provided by the Kalman estimator 13.

According to preferred embodiments of the invention, the commandsteering wheel angle calculation unit 25 calculates the command steeringwheel angle using input information, for example four types of inputinformation, such as, but not limited to, the speed of the vehicle Vwhich is provided by the sensor unit 11, the road curvature ρ_(ref)which is provided by the vehicle location and road curvature calculationunit 12, the yaw rate error e_(γ) which is provided by the secondadjustment unit 24, and information about lateral motion of the vehiclewhich are provided by the Kalman estimator 13.

In particular embodiments, the following Equation [5] is an exemplaryexample of calculating the command steering wheel angle with the sideslip angle β, the measured yaw rate of the vehicle γ, and the relativepath angle Δψ which are preferably provided by the Kalman estimator 13.

$\begin{matrix}{{{\delta_{f} = {{\frac{1}{b_{\delta}}\left\lbrack {{- {f( \cdot )}} - \frac{W_{d}L_{s}}{W_{\gamma}} - {K_{\gamma}e_{\gamma}}} \right\rbrack}W_{d}}},{{W_{\gamma}\mspace{14mu} {and}\mspace{14mu} K_{\gamma}} > 0}}{{{where}\mspace{14mu} b_{\delta}} = {{\frac{C_{f}L_{f}}{I_{zz}} + {\frac{C_{f}}{\overset{\sim}{m}L_{s}}\mspace{14mu} {and}\mspace{14mu} {f( \cdot )}}} = {{C_{\beta}\beta} + {C_{\gamma}\gamma} + {C_{\psi}\Delta \; \psi} - {C_{\rho}{\rho_{ref}.}}}}}} & \lbrack 5\rbrack\end{matrix}$

In detail,

${C_{\beta} = {\frac{{Va}_{11} + {VK}_{d} + {L_{s}a_{21}}}{L_{s}} = {{- \frac{C_{f} + C_{r}}{\overset{\sim}{m}L_{s}}} + \frac{{VK}_{d}}{L_{s}} + \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{I_{zz}}}}},{C_{\gamma} = {\frac{{Va}_{12} + V + {K_{d}L_{s}} + {L_{s}a_{22}}}{L_{s}} = {\frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{\overset{\sim}{m}{VL}_{s}} + K_{d} - \frac{{C_{r}L_{r}^{2}} + {C_{f}L_{f}^{2}}}{I_{zz}V}}}},{C_{\psi} = \frac{K_{d}V}{L_{s}}},{{{and}\mspace{14mu} C_{\rho}} = {\frac{V^{2}}{L_{s}}.}}$

Further, K_(d), W_(d), K_(γ), and W_(γ) are variable control gains.

Accordingly, the command steering wheel angle calculation unit 25suitably calculates the command steering wheel angle using the variablecontrol gains and the control variables C_(β), C_(γ), C_(ψ) and C_(ρ).

According to further preferred embodiments, the third adjustment unit 26suitably generates the compensated command steering wheel angle, whichis the sum of the command steering wheel angle δ_(fo) provided by thecommand steering wheel angle calculation unit 25 and the steering wheelcontortion angle δ_(o) provided by the steering wheel contortion anglecalculation unit 30.

Preferably, the steering contortion warning unit 40 may visually,aurally or tactually provide a warning for the distortion of thesteering wheel in the case where the number of times that the steeringwheel contortion angle δ_(o) exceeds a predetermined reference angle isequal to or greater than a predetermined number.

The present invention provides a method for a vehicle to stay in a lanein consideration of a steering wheel contortion angle. According topreferred embodiments of the invention as herein described, the methodcomprising the steps of measuring variables for dynamic characteristicsof a vehicle, and estimating information about lateral motion of thevehicle using the variables for dynamic characteristics of the vehicle,calculating a steering wheel contortion angle δ_(o) using variables fordynamic characteristics of the vehicle and information about lateralmotion of the vehicle, and calculating a desired yaw rate γ_(d) usingvariables for dynamic characteristics of the vehicle and informationabout lateral motion of the vehicle, and calculating a command steeringwheel angle δ_(fo) using the desired yaw rate and the information aboutlateral motion of the vehicle, and generating a compensated commandsteering wheel angle, which is a sum of the command steering wheel angleand the steering wheel contortion angle.

Preferably, the variables for dynamic characteristics include, but arenot limited to, information about a road along which the vehicle istraveling, Global Positioning System (GPS) information of the vehicle,the speed of the vehicle V, the measured yaw rate of the vehicle γ, thesteering wheel angle δ_(f), and the side slip angle β.

In preferred embodiments, location of the vehicle, a road curvatureρ_(ref) and a path error d_(s), which are provided the vehicle locationand road curvature calculation unit 12, may be used to estimate theinformation about lateral motion of the vehicle.

Information about lateral motion of the vehicle, which are estimated bya Kalman estimator, include the side slip angle β, the measured yaw rateof the vehicle γ, a path error d_(s), and a relative path angle Δψ.

Preferably, the step of calculating the desired yaw rate γ_(d) furtherincludes a step of calculating a lateral error value, indicating alateral deviation from a center line of the lane, by subtracting thepath error d_(s), which is provided by the Kalman estimator, from areference path error, and a low pass filtering step of controlling asudden motion of the vehicle on a basis of the lateral error value.

Preferably, the step of calculating the command steering wheel angleδ_(fo) is generating a yaw rate error e_(γ)=γ−γ_(d), which is adifference between the desired yaw rate γ_(d), and the measured yaw rateγ, provided by the Kalman estimator, and calculating the commandsteering wheel angle using the yaw rate error e_(γ), and informationabout lateral motion of the vehicle, provided by the Kalman estimator.

FIG. 4 is a graph showing the comparison of the path error of aconventional lane-keeping system with the path error of the lane-keepingsystem according to the present invention. Referring to FIG. 4, it canbe seen that the deviation of an error in lane keeping, occurring due tothe distortion of the steering wheel, can be suitably improved by theabove-described steering wheel contortion angle calculation unit 30.

According to preferred embodiments of the present invention, steeringcontrol and lane keeping control for a vehicle can be performed inconsideration of the steering wheel contortion angle of the vehicle,thus improving the safety and riding comfort of occupants while thevehicle is moving.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A system for keeping a vehicle in a lane in consideration of asteering wheel contortion angle, comprising: an input informationgeneration unit for measuring variables for dynamic characteristics of avehicle, and estimating information about lateral motion of the vehicleusing the variables for dynamic characteristics of the vehicle; asteering wheel contortion angle calculation unit for calculating asteering wheel contortion angle δ_(o) using variables for dynamiccharacteristics of the vehicle and information about lateral motion ofthe vehicle, which are provided by the input information generationunit; and a control unit for calculating a desired yaw rate γ_(d) usingvariables for dynamic characteristics of the vehicle and informationabout lateral motion of the vehicle which are provided by the inputinformation generation unit, and calculating a command steering wheelangle δ_(fo) using the desired yaw rate and the information aboutlateral motion of the vehicle, and generating a compensated commandsteering wheel angle, which is a sum of the command steering wheel angleand the steering wheel contortion angle which is provided by thesteering wheel contortion angle calculation unit.
 2. The systemaccording to claim 1, wherein: the input information generation unitcomprises a sensor unit for measuring variables for dynamiccharacteristics of the vehicle; a vehicle location and road curvaturecalculation unit for calculating a location of the vehicle, a roadcurvature ρ_(ref) and a path error d_(s) using the variables for dynamiccharacteristics of the vehicle which are provided by the sensor unit;and a Kalman estimator for estimating information about lateral motionof the vehicle using the variables for dynamic characteristics of thevehicle which are provided by the sensor unit and the road curvature andthe path error which are provided the vehicle location and roadcurvature calculation unit.
 3. The system according to claim 2, whereinthe variables for dynamic characteristics measured by the sensor unitinclude information about a road along which the vehicle is traveling,Global Positioning System (GPS) information of the vehicle, a speed ofthe vehicle V, a measured yaw rate of the vehicle γ, a steering wheelangle δ_(f), and a side slip angle β.
 4. The system according to claim3, wherein information about lateral motion of the vehicle estimated bythe Kalman estimator include the side slip angle β, the measured yawrate of the vehicle γ, the path error d_(s) and a relative path angleΔψ.
 5. The system according to claim 4, wherein: the Kalman estimatorrealizes an observer equation$\left( {\overset{\overset{\cdot}{\hat{}}}{x} = {{\left( {A - {LC}} \right)\hat{x}} + {Bu} + {Ly}}} \right)$that is configured using a state equation ({dot over (x)}=Ax+Bu)represented by the following equation: $\begin{bmatrix}\overset{\cdot}{\beta} \\\overset{\cdot}{\gamma} \\{\Delta \; \overset{\cdot}{\psi}} \\{\overset{\cdot}{d}s}\end{bmatrix} = {{\begin{bmatrix}a_{11} & a_{11} & 0 & 0 \\a_{11} & a_{11} & 0 & 0 \\0 & 1 & 0 & 0 \\V & L_{s} & V & 0\end{bmatrix}\begin{bmatrix}\beta \\\gamma \\{\Delta \; \psi} \\{ds}\end{bmatrix}} + {\left\lbrack \begin{matrix}b_{11} \\b_{21} \\0 \\0\end{matrix} \middle| \begin{matrix}0 \\0 \\{- V} \\0\end{matrix} \right\rbrack \begin{bmatrix}\delta_{f} \\\rho_{ref}\end{bmatrix}}}$ the Kalman estimator receives the steering wheel angleδ_(f), the measured yaw rate of the vehicle γ from the sensor unit andthe road curvature ρ_(ref), the path error d_(s) from the vehiclelocation and road curvature calculation unit, and calculates estimatedstate variables by which eigenvalues of a matrix (A−LC) are negativevalues, thus estimating the side slip angle β, the measured yaw rate ofthe vehicle γ, the path error d_(s) and the relative path angle Δψ,where${a_{11} = {- \frac{C_{f} + C_{r}}{\overset{\sim}{m}V}}},{a_{12} = {{- 1} + \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{\overset{\sim}{m}V^{2}}}},{a_{21} = \frac{{C_{r}L_{r}} - {C_{f}L_{f}}}{I_{zz}}},{a_{22} = {- \frac{{C_{r}L_{r}^{2}} + {C_{f}L_{f}^{2}}}{I_{zz}V}}},{b_{11} = \frac{C_{f}}{\overset{\sim}{m}V}},{{{and}\mspace{14mu} b_{21}} = \frac{C_{f}L_{f}}{I_{zz}}},{and}$where constants of respective elements are defined as follows: C_(f):cornering stiffness of a front wheel shaft of the vehicle, L_(f):distance from a center of gravity of the vehicle to the front wheelshaft, C_(r): cornering stiffness of a rear wheel shaft of the vehicle,L_(r): distance from a center of gravity of the vehicle to the rearwheel shaft, V: vehicle speed, {tilde over (m)}: virtual vehicle weight(weight of vehicle (m)/road friction coefficient (μ)), L_(s): distancebetween the center of gravity of the vehicle and a GPS installed in thevehicle, I_(zz): moment of inertia of the vehicle, δ_(f): steering wheelangle, and ρ_(ref): lane curvature.
 6. The system according to claim 4,wherein the steering wheel contortion angle calculation unit calculatesthe steering wheel contortion angle using steering wheel angle δ_(f)which is provided by the sensor unit and the side slip angle β, themeasured yaw rate of the vehicle γ which are provided by the Kalmanestimator.
 7. The system according to claim 6, wherein the steeringwheel contortion angle calculation unit calculates the steering wheelcontortion angle using an observer equation$\left( {{\overset{\overset{\cdot}{\hat{}}}{x}}_{o} = {{\left( {A_{o} - {L_{o}C_{o}}} \right){\hat{x}}_{o}} + {B_{o}u_{o}} + {L_{o}y_{o}}}} \right)$of a state equation ({dot over (x)}_(o)=A_(o)x_(o)+B_(o)u_(o), wherey_(o)=C_(o)x_(o)=[0 1 0]x_(o)) represented by the following equation:$\begin{bmatrix}\overset{\cdot}{\beta} \\\overset{\cdot}{\gamma} \\{\overset{\cdot}{\delta}}_{o}\end{bmatrix} = {{\begin{bmatrix}a_{11} & a_{12} & {- b_{11}} \\a_{21} & a_{22} & {- b_{21}} \\0 & 0 & 0\end{bmatrix}\begin{bmatrix}\beta \\\gamma \\\delta_{0}\end{bmatrix}} + {{\begin{bmatrix}b_{11} \\b_{21} \\0\end{bmatrix}\left\lbrack \delta_{f} \right\rbrack}.}}$
 8. The systemaccording to claim 4, wherein the control unit includes a desired yawrate calculation unit for calculating a desired yaw rate γ_(d) on abasis of the speed of the vehicle V which is provided by the sensorunit, information about lateral motion of the vehicle which are providedby the Kalman estimator, and a predetermined distance L_(s) between acenter of gravity of the vehicle and a Global Positioning System (GPS)installed in the vehicle;
 9. The system according to claim 8, whereinthe desired yaw rate calculation unit includes a first adjustment unitfor calculating a lateral error value, indicating a lateral deviationfrom a center line of the lane, by subtracting the path error d_(s),which is provided by the Kalman estimator, from a reference path error,and a low pass filter unit for controlling a sudden motion of thevehicle on a basis of the lateral error value which is provided by thefirst adjustment unit.
 10. The system according to claim 8, wherein: thecontrol unit includes a second adjustment unit for generating a yaw rateerror e_(γ)=γ−γ_(d), which is a difference between the desired yaw rateγ_(d), provided by the desired yaw rate calculation unit, and themeasured yaw rate γ, provided by the Kalman estimator; a commandsteering wheel angle calculation unit for calculating the commandsteering wheel angle using the yaw rate error e_(γ), provided by thesecond adjustment unit, and information about lateral motion of thevehicle, provided by the Kalman estimator; and a third adjustment unitfor generating the compensated command steering wheel angle, which isthe sum of the command steering wheel angle δ_(fo), provided by thecommand steering wheel angle calculation unit, and the steering wheelcontortion angle δ_(fo), provided by the steering wheel contortion anglecalculation unit.
 11. The system according to claim 1, furthercomprising a steering contortion warning unit for providing a warningfor distortion of a steering wheel using any one of a visual manner, anaural manner, and a tactual manner, or a combination thereof if a numberof times that the steering wheel contortion angle δ_(o) exceeds apredetermined reference angle is equal to or greater than apredetermined number.
 12. A method for keeping a lane in considerationof a steering wheel contortion angle, the method comprising the stepsof: measuring variables for dynamic characteristics of a vehicle, andestimating information about lateral motion of the vehicle using thevariables for dynamic characteristics of the vehicle; calculating asteering wheel contortion angle δ_(o) using variables for dynamiccharacteristics of the vehicle and information about lateral motion ofthe vehicle; and calculating a desired yaw rate γ_(d) using variablesfor dynamic characteristics of the vehicle and information about lateralmotion of the vehicle, and calculating a command steering wheel angleδ_(fo) using the desired yaw rate and the information about lateralmotion of the vehicle, and generating a compensated command steeringwheel angle, which is a sum of the command steering wheel angle and thesteering wheel contortion angle.
 13. The method according to claim 12,wherein the variables for dynamic characteristics include informationabout a road along which the vehicle is traveling, Global PositioningSystem (GPS) information of the vehicle, a speed of the vehicle V, ameasured yaw rate of the vehicle γ, a steering wheel angle δ_(f), and aside slip angle β, and information about lateral motion of the vehicle,which are estimated by a Kalman estimator, include the side slip angleβ, the measured yaw rate of the vehicle γ, a path error d_(s) and arelative path angle Δψ.
 14. The method according to claim 13, whereinthe step of calculating the desired yaw rate γ_(d) further includes astep of calculating a lateral error value, indicating a lateraldeviation from a center line of the lane, by subtracting the path errord_(s), which is provided by the Kalman estimator, from a reference patherror, and a low pass filtering step of controlling a sudden motion ofthe vehicle on a basis of the lateral error value.
 15. The methodaccording to claim 14, wherein the step of calculating the commandsteering wheel angle δ_(fo) is generating a yaw rate errore_(γ)=γ−γ_(d), which is a difference between the desired yaw rate γ_(d),and the measured yaw rate γ, provided by the Kalman estimator, andcalculating the command steering wheel angle using the yaw rate errore_(γ), and information about lateral motion of the vehicle, provided bythe Kalman estimator.
 16. A system for keeping a vehicle in a lane inconsideration of a steering wheel contortion angle, comprising: an inputinformation generation unit; a steering wheel contortion anglecalculation unit; and a control unit for calculating a desired yaw rateγ_(d) using variables for dynamic characteristics of the vehicle andinformation about lateral motion of the vehicle which are provided bythe input information generation unit.
 17. The system of claim 16,wherein the input information generation unit is used for measuringvariables for dynamic characteristics of a vehicle using the variablesfor dynamic characteristics of the vehicle.
 18. The system of claim 16,wherein the input information generation unit is used for estimatinginformation about lateral motion of the vehicle using the variables fordynamic characteristics of the vehicle.
 19. The system of claim 16,wherein the steering wheel contortion angle calculation unit is used forcalculating a steering wheel contortion angle δ_(o) using variables fordynamic characteristics of the vehicle and information about lateralmotion of the vehicle.
 20. The system of claim 20, wherein the variablesfor dynamic characteristics of the vehicle and information about lateralmotion of the vehicle are provided by the input information generationunit.
 21. The system of claim 16, further comprising calculating acommand steering wheel angle δ_(fo) using the desired yaw rate and theinformation about lateral motion of the vehicle, and generating acompensated command steering wheel angle.
 22. The system of claim 21,wherein the compensated command steering wheel angle is a sum of thecommand steering wheel angle and the steering wheel contortion angle,which is provided by the steering wheel contortion angle calculationunit.
 23. A motor vehicle comprising the system for keeping a vehicle ina lane in consideration of a steering wheel contortion angle of claim 1.24. A motor vehicle comprising the system for keeping a vehicle in alane in consideration of a steering wheel contortion angle of claim 16.